Power storage device

ABSTRACT

The present invention relates to a power storage device including: a positive electrode having a positive-electrode current collector, a positive-electrode active material with a plurality of first projections on the positive-electrode current collector, and a first insulator on an end of each of the plurality of first projections; a negative electrode having a negative-electrode current collector, a negative-electrode active material with a plurality of second projections on a surface of the negative-electrode current collector, and a second insulator on an end of each of the plurality of second projections; a separator between the positive electrode and the negative electrode; and an electrolyte provided in a space between the positive electrode and the negative electrode and containing carrier ions. In each of the first projections and the second projections, a ratio of the height to the width is 3 or more and 1000 or less to 1, i.e. (3 to 1000):1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/719,629, filed Mar. 8, 2010, now allowed, which claims the benefit ofa foreign priority application filed in Japan as Serial No. 2009-054519on Mar. 9, 2009, both of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed in this specification relates to power storagedevices.

2. Description of the Related Art

In recent years, power storage devices, such as lithium-ion secondarybatteries, which are power storage devices where carbon or lithium metaloxide is used as a battery material and which are charged and dischargedby the movement of lithium ions as carrier ions between a positiveelectrode and a negative electrode, and electrochemical capacitors, havebeen actively developed (see References 1 to 3).

REFERENCES [Reference 1] Japanese Published Patent Application No.2008-294314 [Reference 2] Japanese Published Patent Application No.2002-289174 [Reference 3] Japanese Published Patent Application No.2007-299580 SUMMARY OF THE INVENTION

In order to obtain a power storage device with high capacity, thesurface areas of a positive electrode and a negative electrode should beincreased. The surface areas of a positive electrode and a negativeelectrode can be increased by providing a surface of each of thepositive electrode and the negative electrode with projections anddepressions.

A high-capacity power storage device can be obtained by interposing aseparator between a positive electrode and a negative electrode havingprojections and depressions and by providing an electrolyte between thepositive electrode and the negative electrode.

However, the positive or negative electrode may expand due to charging,and with that pressure, the separator may be broken and defective shortcircuit may be caused.

In addition, if pressure is applied to a separator between a positiveelectrode and a negative electrode in a thin, small-sized power storagedevice, the separator may easily be broken.

In the present invention, a surface of each of a positive-electrodeactive material and a negative-electrode active material is providedwith a plurality of projections, and on an end of each of theprojections, an insulator is disposed to relieve pressure that is to beapplied to a separator.

An embodiment of the present invention relates to a power storage deviceincluding: a positive electrode having a positive-electrode currentcollector, a positive-electrode active material with a plurality offirst projections on the positive-electrode current collector, and afirst insulator on an end of each of the plurality of first projections;a negative electrode having a negative-electrode current collector, anegative-electrode active material with a plurality of secondprojections on the negative-electrode current collector, and a secondinsulator on an end of each of the plurality of second projections; aseparator between the positive electrode and the negative electrode; andan electrolyte provided in a space between the positive electrode andthe negative electrode and containing carrier ions. In each of the firstprojections and the second projections, a ratio of the height to thewidth is 3 or more and 1000 or less to 1, i.e. (3 to 1000):1.

Each of the first insulator and the second insulator may be any one of,or a stacked layer of two or more of, an acrylic resin, a polyimideresin, a polyimide amide resin, a phenol resin, an epoxy resin, aresist, a silicon oxide film, a silicon oxide film containing nitrogen,a silicon nitride film containing oxygen, and a silicon nitride film.

The carrier ions may be alkali metal ions or alkaline earth metal ions.The alkali metal ions may be lithium (Li) ions or sodium (Na) ions, andthe alkaline earth metal ions may be magnesium (Mg) ions or calcium (Ca)ions.

Because the surface of each of the positive-electrode active materialand the negative-electrode active material is provided with theplurality of projections, the surface area is increased and a thin,small-sized power storage device with high capacity can be obtained.

Furthermore, because the insulator is provided on each of the pluralityof projections, even when pressure is applied between the positiveelectrode and the negative electrode, the insulator absorbs or dispersesthe pressure so as to prevent breaking of the separator. Accordingly, ahighly reliable power storage device can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a manufacturing process ofa power storage device.

FIGS. 2A to 2D are cross-sectional views illustrating a manufacturingprocess of a power storage device.

FIGS. 3A to 3D are cross-sectional views illustrating a manufacturingprocess of a power storage device.

FIGS. 4A and 4B are a perspective view and a cross-sectional view of apower storage device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention disclosed in this specification will behereinafter described with reference to the accompanying drawings. Notethat the invention disclosed in this specification can be carried out ina variety of different modes, and it is easily understood by thoseskilled in the art that the modes and details of the invention disclosedin this specification can be changed in various ways without departingfrom the spirit and scope thereof. Therefore, the invention disclosed inthis specification should not be interpreted as being limited to thedescription in the embodiments. Note that in the accompanying drawings,the same portions or portions having similar functions are denoted bythe same reference numerals, and repetitive description thereof isomitted.

Embodiment 1

This embodiment is described with reference to FIG. 1, FIGS. 2A to 2D,FIGS. 3A to 3D, and FIGS. 4A and 4B.

First, a plate-like positive-electrode current collector 111 is prepared(see FIG. 2A). As the positive-electrode current collector 111, a simplesubstance, such as aluminum (Al) or titanium (Ti), or a compound thereofmay be used.

Next, a plate-like positive-electrode active material 101 which is amaterial of a positive-electrode active material 112 is formed over thepositive-electrode current collector 111 (see FIG. 2B).

As the plate-like positive-electrode active material 101, a metalcompound (oxide, sulfide, or nitride) having a layered structure can beused. In addition, as the positive-electrode active material 112 for acapacitor, activated carbon can be used. Furthermore, as thepositive-electrode active material 112 for a lithium-ion secondarybattery where lithium ions are used as carrier ions, alithium-containing composite oxide represented by a chemical formulaLi_(x)M_(y)O₂ (note that M represents Co, Ni, Mn, V, Fe, or Ti, and x isin the range of from 0.2 to 2.5 and y is in the range of from 0.8 to1.25), such as LiCoO₂ or LiNiO₂, may be used. Note that in the casewhere the aforementioned lithium-containing composite oxide representedby the chemical formula Li_(x)M_(y)O₂ is used as the positive-electrodeactive material 112 of a lithium-ion secondary battery, M may includeeither one element or two or more elements. In other words, as thepositive-electrode active material 112 of a lithium-ion secondarybattery, a multi-element, lithium-containing composite oxide may beused.

Over the plate-like positive-electrode active material 101, a pluralityof insulators 113 serving as a mask in an etching step are formed (seeFIG. 2C).

Examples of the insulators 113 include organic resins such as an acrylicresin, a polyimide resin, a polyimide amide resin, a phenol resin, anepoxy resin, and a resist. The insulators 113 may be formed with such anorganic resin by a printing method, a spin-coating method, or the like.For example, the insulators 113 may be formed as follows: unexposedphotosensitive acrylic is formed over a surface of the plate-likepositive-electrode active material 101 by a printing method and regionswhere the insulators 113 are to be formed are exposed to light.

Alternatively, an inorganic insulating material, such as a silicon oxidefilm, a silicon oxide film containing nitrogen, a silicon nitride filmcontaining oxygen, or a silicon nitride film, may be used for theinsulators 113.

Further alternatively, a single layer of the aforementioned organicresin or inorganic insulating material, a stacked layer of two or moreof the organic resins or a stacked layer of two or more of the inorganicinsulating materials, or a stacked layer of two or more of the organicresins and the inorganic insulating materials may be used for theinsulators 113.

Next, with the use of the insulators 113 as a mask, the plate-likepositive-electrode active material 101 is anisotropically etched by adry etching method. Accordingly, the positive-electrode active material112 is formed, which includes a plurality of projections 115 in which aratio of height h to width a is 3 or more and 1000 or less to 1, i.e. (3to 1000):1, preferably 10 or more and 1000 or less to 1, i.e. (10 to1000):1. For example, each of the projections 115 has a width a of 1 μmto 10 μm and a height b of 3 μm to 1000 μm, preferably, a width a of 1μm to 10 μm and a height b of 10 μm to 100 μm, or a width a of 1 μm anda height b of 10 μm (see FIG. 2D). FIG. 2D is a cross-sectional view, inwhich the positive-electrode active material 112 is illustrated ashaving a comb-like shape. However, the projections 115 are also formedin rows behind those illustrated, and thus, the positive-electrodeactive material 112 has a shape like a pin frog (spikes).

In the case of using a plate-like positive-electrode active material 101which is difficult to etch by dry etching, the projections 115 may beformed by a different method such as mechanical processing, screenprinting, electroplating, or hot embossing. Even in the case of using aplate-like positive-electrode active material 101 which can be etched bydry etching, the projections 115 may be formed by any of these methods.In the above manner, a positive electrode 117 is formed.

On the other hand, a plate-like negative-electrode current collector 121is prepared (see FIG. 3A). As the negative-electrode current collector121, a simple substance, such as copper (Cu), aluminum (Al), nickel(Ni), or titanium (Ti), or a compound thereof may be used.

Next, a plate-like negative-electrode active material 105 which is amaterial of a negative-electrode active material 122 is formed over thenegative-electrode current collector 121 (see FIG. 3B).

As the plate-like negative-electrode active material 105, a lithium-ionholding body such as a carbon material, a silicon material, or a siliconalloy material, which is capable of occluding and releasing lithiumions, is used. As such a carbon material, powdered or fibrous graphiteor the like can be used. As such a silicon material, a material obtainedby depositing microcrystalline silicon and then removing amorphoussilicon from the microcrystalline silicon by etching may be used. Whenamorphous silicon is removed from microcrystalline silicon, the surfacearea of the remaining microcrystalline silicon is increased. In alithium-ion capacitor where lithium ions are used as carrier ions, forexample, a material obtained by impregnating the aforementionedlithium-ion holding body with metallic lithium may be used. In otherwords, a material obtained by impregnating the aforementioned carbonmaterial, silicon material, silicon alloy material, or the like withmetallic lithium may be used as the negative-electrode active material122.

Next, over the plate-like negative-electrode active material 105, aplurality of insulators 123 serving as an etching mask are formed (seeFIG. 3C). The insulators 123 may be formed with a material and by amanufacturing method which are similar to those of the insulators 113.

Next, with the use of the insulators 123 as a mask, the plate-likenegative-electrode active material 105 which can be etched by dryetching is anisotropically etched by a dry etching method. Accordingly,the negative-electrode active material 122 is formed, which includes aplurality of projections 125 in which a ratio of height d to width c is3 or more and 1000 or less to 1, i.e. (3 to 1000):1, preferably 10 ormore and 1000 or less to 1, i.e. (10 to 1000):1. For example, each ofthe projections 125 has a width c of 1 μm to 10 μm and a height d of 3μm to 1000 μm, preferably, a width c of 1 μm to 10 μm and a height d of10 μm to 100 μm, or a width c of 1 μm and a height d of 10 μm (see FIG.3D). FIG. 3D is a cross-sectional view, in which the negative-electrodeactive material 122 is illustrated as having a comb-like shape. However,the projections 125 are also formed in rows behind those illustrated,and thus, the negative-electrode active material 122 has a shape like apin frog (spikes).

In the case of using a plate-like negative-electrode active material 105which is difficult to etch by dry etching, the projections 125 may beformed by a different method such as mechanical processing, screenprinting, electroplating, or hot embossing. Even in the case of using aplate-like negative-electrode active material 105 which can be etched bydry etching, the projections 125 may be formed by any of these methods.In the above manner, a negative electrode 127 is formed.

Next, the positive electrode 117 and the negative electrode 127 aredisposed to face each other, and a separator 131 is provided between thepositive electrode 117 and the negative electrode 127.

As the separator 131, paper, nonwoven fabric, a glass fiber, a syntheticfiber such as nylon (polyamide), vinylon (also called vinalon) (apolyvinyl alcohol based fiber), polyester, acrylic, polyolefin, orpolyurethane, or the like may be used. Note that a material which doesnot dissolve in an electrolyte 132 mentioned below should be selected.

More specific examples of materials of the separator 131 arehigh-molecular compounds based on fluorine-based polymer, polyether suchas polyethylene oxide and polypropylene oxide, polyolefin such aspolyethylene and polypropylene, polyacrylonitrile, polyvinylidenechloride, polymethyl methacrylate, polymethylacrylate, polyvinylalcohol, polymethacrylonitrile, polyvinyl acetate, polyvinylpyrrolidone,polyethyleneimine, polybutadiene, polystyrene, polyisoprene, andpolyurethane, derivatives thereof, cellulose, paper, and nonwovenfabric, which can be used either alone or in combination.

The separator 131 is interposed between the projections 115 of thepositive-electrode active material 112 and the projections 125 of thenegative-electrode active material 122 and thus may be broken byapplication of pressure. However, because the insulators 113 areprovided on the projections 115 and the insulators 123 are provided onthe projections 125, the insulators 113 and the insulators 123 absorb orsuppress pressure and can prevent the separator 131 from being broken.Accordingly, the positive electrode 117 and the negative electrode 127can be prevented from being in contact with each other andshort-circuited.

The electrolyte 132 is provided in a space between the positiveelectrode 117 and the negative electrode 127. Through the above process,a power storage device 135 is manufactured (see FIG. 1).

The electrolyte 132 contains alkali metal ions as carrier ions, such aslithium ions, and the lithium ions are responsible for electricalconduction. The electrolyte 132 includes a solvent and a lithium saltwhich dissolves in the solvent. Examples of lithium salts include LiPF₆(lithium hexafluorophosphate), LiClO₄, LiBF₄, LiAlCl₄, LiSbF₆, LiSCN,LiCl, LiCF₃SO₃, LiCF₃CO₂, Li(CF₃SO₂)₂, LiAsF₆, LiN(CF₃SO₂)₂, LiB₁₀Cl₁₀,LiN(C₂F₅SO₂), LiPF₃(CF₃)₃, LiPF₃(C₂F₅)₃, and the like, which can be usedfor the electrolyte 132, either alone or in combination.

Note that in the description of this specification, alkali metal ionssuch as lithium (Li) ions are used as carrier ions; instead of lithiumions, alkali metal ions such as sodium (Na) ions may be used.Furthermore, alkaline earth metal ions such as magnesium (Mg) ions orcalcium (Ca) ions may be used.

In the case of manufacturing a capacitor where such carrier ions areused and the negative-electrode active material 122 is impregnated witha metal of the same kind as that of the carrier ions, the aforementionedcarbon material, silicon material, silicon alloy material, or the like,which is capable of occluding and releasing the carrier ions, may beimpregnated with the metal.

Examples of the solvent of the electrolyte 132 include: cycliccarbonates such as ethylene carbonate (hereinafter abbreviated as EC),propylene carbonate (PC), butylene carbonate (BC), and vinylenecarbonate (VC); acyclic carbonates such as dimethyl carbonate (DMC),diethyl carbonate (DEC), ethylmethyl carbonate (hereinafter abbreviatedas EMC), methylpropyl carbonate (MPC), methylisobutyl carbonate (MIPC),and dipropyl carbonate (DPC); aliphatic carboxylic acid esters such asmethyl formate, methyl acetate, methyl propionate, and ethyl propionate;γ-lactones such as γ-butyrolactone; acyclic ethers such as1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), and ethoxymethoxyethane (EME); cyclic ethers such as tetrahydrofuran and2-methyltetrahydrofuran; dimethylsulfoxide; 1,3-dioxolane; alkylphosphate esters such as trimethyl phosphate, triethyl phosphate, andtrioctyl phosphate and fluorides thereof. These materials can be usedeither alone or in combination.

The power storage device 135 manufactured in the above manner may beused with a substrate 137 attached to its surface, if necessary (seeFIG. 4B). As the substrate 137, a substrate which functions as a sealinglayer may be selected, or a substrate which functions as a protector maybe selected. Furthermore, a substrate which functions as both a sealinglayer and a protector may be selected, or a substrate which functions asa sealing layer and a substrate which functions as a protector may bestacked.

The power storage device 135 may be used in a long plate-like shape, orthe power storage device 135 in a long plate-like shape may be rolledinto a cylindrical power storage device 138, if necessary (see FIG. 4A).Note that FIG. 4B is a cross-sectional view taken along a line A-A′ ofFIG. 4A.

This application is based on Japanese Patent Application serial no.2009-054519 filed with Japan Patent Office on Mar. 9, 2009, the entirecontents of which are hereby incorporated by reference.

1. (canceled)
 2. A method for manufacturing a power storage devicecomprising steps of: forming a plate-like positive-electrode activematerial on a positive-electrode current collector; forming a pluralityof first insulators on the plate-like positive-electrode activematerial; etching the plate-like positive-electrode active materialusing the plurality of first insulators as masks, thereby forming apositive electrode having a positive-electrode active material with aplurality of first projections, wherein each of the plurality of firstinsulators is provided on an end of each of the plurality of firstprojections; forming a plate-like negative-electrode active material ona negative-electrode current collector; forming a plurality of secondinsulators on the plate-like negative-electrode active material; etchingthe plate-like negative-electrode active material using the plurality ofsecond insulators as masks, thereby forming a negative electrode havinga negative-electrode active material with a plurality of secondprojections, wherein each of the plurality of second insulators isprovided on an end of each of the plurality of second projections;providing a separator between the positive electrode and the negativeelectrode; and providing an electrolyte in a space between the positiveelectrode and the negative electrode, the electrolyte containing carrierions.
 3. The method according to claim 2, wherein a width of each of theplurality of first projections is smaller than a height of each of theplurality of first projections, and wherein a width of each of theplurality of second projections is smaller than a height of each of theplurality of second projections.
 4. The method according to claim 3,wherein in each of the plurality of first projections and the pluralityof second projections, a ratio of the height to the width is 3 or moreand 1000 or less to
 1. 5. The method according to claim 2, wherein thepositive-electrode current collector comprises any one of aluminum,titanium, and a compound thereof.
 6. The method according to claim 2,wherein the positive-electrode active material comprises any one of ametal compound having a layered structure, activated carbon, and alithium-containing composite oxide.
 7. The method according to claim 2,wherein the negative-electrode current collector comprises any one ofcopper, aluminum, nickel, titanium, and a compound thereof
 8. The methodaccording to claim 2, wherein the negative-electrode active materialcomprises any one of carbon material, silicon material, and siliconalloy material.
 9. The method according to claim 2, wherein each of theplurality of first insulators and the plurality of second insulatorscomprises at least one of acrylic resin, polyimide resin, polyimideamide resin, phenol resin, epoxy resin, resist, silicon oxide, siliconoxide containing nitrogen, silicon nitride containing oxygen, andsilicon nitride.
 10. The method according to claim 2, wherein theseparator includes any one of cellulose, paper, nonwoven fabric, glassfiber, nylon, polyamide, vinylon, polyester, acrylic, polyolefin,polyurethane, fluorine-based polymer, polyethylene, polypropylene,polyethylene oxide, polypropylene oxide, polyacrylonitrile,polyvinylidene chloride, polymethyl methacrylate, polymethylacrylate,polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate,polyvinylpyrrolidone, polyethyleneimine, polybutadiene, polystyrene,polyisoprene, and derivatives thereof.
 11. The method according to claim2, wherein a solvent of the electrolyte includes any one of cycliccarbonate, ethylene carbonate, propylene carbonat, butylene carbonate,vinylene carbonate, acyclic carbonate, dimethyl carbonate, diethylcarbonate, ethylmethyl carbonate, methylpropyl carbonate, methylisobutylcarbonate, dipropyl carbonate, aliphatic carboxylic acid ester, methylformate, methyl acetate, methyl propionate, ethyl propionate,γ-lactones, γ-butyrolactone, acyclic ether, 1,2-dimethoxyethane,1,2-diethoxyethane, ethoxymethoxy ethane, cyclic ether, tetrahydrofuran,2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, alkylphosphate ester, trimethyl phosphate, triethyl phosphate, and trioctylphosphate and fluorides thereof
 12. A method for manufacturing a powerstorage device comprising steps of: forming a first-electrode activematerial on a first-electrode current collector; forming a plurality offirst insulators on the first-electrode active material; and etching thefirst-electrode active material using the plurality of first insulatorsas masks, thereby forming a first electrode having a first-electrodeactive material with a plurality of first projections, wherein each ofthe plurality of first insulators is provided on an end of each of theplurality of first projections.
 13. The method according to claim 12,wherein the first electrode is a positive electrode.
 14. The methodaccording to claim 12, wherein the first electrode is a negativeelectrode.
 15. The method according to claim 12, wherein each of theplurality of first insulators has a curved upper surface and a flatbottom surface.
 16. The method according to claim 12, further comprisingsteps of: forming a second-electrode active material on asecond-electrode current collector; forming a plurality of secondinsulators on the second-electrode active material; and etching thesecond-electrode active material using the plurality of secondinsulators as masks, thereby forming a second electrode having asecond-electrode active material with a plurality of second projections.17. The method according to claim 16, further forming a separatorbetween the first electrode and the second electrode, wherein a firstsurface of the separator is in contact with the plurality of firstinsulators and a second surface of the separator is in contact with theplurality of second insulators.
 18. The method according to claim 12,wherein a width of each of the plurality of first projections is smallerthan a height of each of the plurality of first projections.
 19. Themethod according to claim 18, wherein in each of the plurality of firstprojections, a ratio of the height to the width is 3 or more and 1000 orless to 1.